1. Field of the Invention
This invention relates to a grinding method and apparatus, and more particularly to a grinding method adapted to enclose objects to be ground and a grinding material in a grinding barrel and give the grinding barrel a variety of motions to grind the objects to be ground, and a grinding apparatus for implementing such a method.
2. Description of the Prior Art
A conventional grinding method adapted to enclose objects to be ground and a grinding material in a grinding barrel and give the grinding barrel a variety of motions, that is, a so-called barrel grinding method employs a grinding barrel which is axially supported by a carrier or a drum, where the center of the grinding barrel is positioned concentrically with the rotating shaft about which the grinding barrel is rotated. The grinding barrel is rotated by a driving unit or rotated in the same direction as a drum to produce a centrifugal force to thereby perform a grinding process. In either case, the grinding barrel is rotated with the center thereof as the rotating axis, whereby objects to be ground and a grinding material in the grinding barrel are subjected to a repetition of identical circular motions or fixed motions. For this reason, only an upper portion of a mass of the objects to be ground and the grinding material can be agitated by an avalanche phenomenon to grind the objects to be ground.
The above-mentioned grinding method, however, implies a number of problems such as a lack of uniformity in finished products, residue of the grinding materials in recesses, curved surfaces, rear surfaces and so on, bruises on the surfaces of ground objects, and so on. Furthermore, the grinding method as mentioned above is not capable of providing a sufficiently high quality of grinding even if the rotational speed of the grinding barrel is decreased to grind the objects for a long time.
Generally, the above-mentioned grinding barrel is constructed such that the diameter and the length thereof are chosen to be the same size. Such a construction may cause objects being ground to overlap each other, and accordingly a number of bruises are produced on the surface of ground objects. To solve this problem due to the construction of the grinding barrel, there have been proposed a grinding barrel having the diameter and the length different from each other and a method of rotating a grinding barrel in forward and backward directions.
However, in such alternate rotations of the grinding barrel in the forward and backward directions, gears and pulleys for rotating the grinding barrel may be damaged by shocks given to these elements when the rotation is changed from the forward direction to the backward direction and vice versa. For this reason, if the rotational speed of the grinding barrel is decreased, the grinding process takes a long time, thereby rendering it impossible to completely prevent bruises on the surfaces of ground objects.
Further, the above mentioned grinding barrel generally comprises a single chamber therein and one to four grinding barrels are mounted on a drum. The internal chamber of the barrel is appropriately re-shaped in accordance with the necessity for providing an optimal grinding for objects to be ground.
The conventional grinding barrel as mentioned above, however, comprises a single internal chamber and the volume thereof is definite, so that it is difficult to grind a large number of different objects in a small quantity or precisely grind a heavy-weight or a large-volume object in such a barrel. In addition, a troublesome time-consuming exchange is necessary every time a different grinding is to be performed. It is also difficult to precisely finish the surface of grounded objects due to bruises caused by collisions and contacts of objects being grounded.